This invention relates to the preparation of ketones having at least 6 carbon atoms by the catalysed condensation reaction of other ketones. In particular the present invention relates to the use of metal-doped polysulfonated ion exchange resin catalysts to provide the desired ketones in greater yield and selectivity compared to the condensation catalysts previously used.
Aldol condensation reactions involve the dimerization of a carbonyl compound (aldehyde or ketone) by the addition of the α-carbon of one carbonyl compound to the carbonyl carbon of another to provide a β-hydroxy carbonyl compound. In the case of the condensation of two ketones in the presence of an acidic catalyst, dehydration usually occurs subsequent to dimerization to provide an α,β-unsaturated ketone; reduction of the double bond using conventional techniques may be used to provide the saturated ketone adduct.
For example, U.S. Pat. No. 6,008,416 discloses a working example of dimerization/dehydration/hydrogenation of acetone to provide mesityl oxide, and ultimately methyl isobutyl ketone (MIBK), by using a monosulfonated acidic catalyst (Amberlyst™ 15 ion exchange resin) loaded with 0.05% palladium. The sulfonic acid group acts as a condensation/dehydration catalyst and the palladium acts as catalyst for hydrogenation of the double bond.
The problem addressed by the present invention is to overcome the deficiencies of prior methods for the preparation of ketones by use of selected catalyst materials to provide enhanced yields and selectivities to desired saturated ketone adducts.